使用扩散张量成像数据重建脑白质纤维的新算法

由磁共振扩散张量成像（DT-MRI）可以获得扩散的方向性信息，利用这些信息可以无创地重建人脑的白质纤维，而且这也是目前在活体上重建脑白质纤维的唯一方法．然而由于磁共振成像设备与成像技术的限制，纤维重建过程中会遇到许多困难，例如：DT-MRI的数据是离散的，而所要重建的纤维是连续的；而且由相对较低的MRI空间分辨率所引起的部分容积效应会影响DT—MRI的数据质量．针对这些问题，提出了一种加权跟踪算法．该算法结合经典物理理论，利用纤维跟踪过程中待定方向点周围相关体元的主向量与分量各向异性（FA）值来计算纤维跟踪线的前进方向．实验表明，该算法能够相对较好地解决重建过程中所存在的困难．从重建的效果看，该方法能够很好地反映脑白质纤维的分布情况．     

预压力对纵扭复合压电超声马达共振频率影响的研究

研究了预压力对超声马达共振频率的影响.通过对纵扭复合型压电超声马达运行机理的研究,分析了预压力与纵扭复合型压电超声马达纵扭振子输出压电应力协同作用的机理.理论和实验研究结果表明,纵纽复合型压电超声马达的共振频率随预压力增加而增加;马达预压力和共振频率存在正比关系.理论分析和实验测试结果符合较好.     

Multiple Resonance and Stability of a Motor-elastic Linkage Mechanism System

IntroductionThe use of high-speed,light-weight mechanic trans mi-ssion systems in modernindustries under the requirement ofprecise positioning has increased interest in the researchesinto dynamics and stability of mechanic trans missionsystems . As a result , there are a significant number ofstudies on dynamics and stability of mechanis m and manyuseful conclusions have been obtained[1 3]. But the effectsof drive motors on the dynamic characters of mechanis mswere not discussed in these studie…     

核四极矩共振炸药探测原理与试验

为了解决探雷虚警率，实现探雷的有效性，介绍了核四极矩共振（Nuclear quadrupole resonance简称NQR）基本原理及其用于炸药探测的依据；分析了黑索金（RDX）、梯恩梯（TNT）分子中氮原子（N^14）的共振频率及其探测原理；介绍了一种可行的炸药探测研究试验系统，重点研究分析了黑索金（RDX）自由感应衰减（FID）信号、FFT变换、频率响应以及不同质量的RDX对探测信号的影响。实现了RDX的有效探测。     

罗丹明B-硫氰酸钾共振光散射测定三苯基锡

酸性介质中,三苯基锡化合物与硫氰酸钾和罗丹明B相互作用会产生共振光散射(RLS)增强信号,在250~500 nm波长范围内有两个散射峰,分别位于329.2 nm和370 nm处,其中最大散射峰位于329.2 nm处.考察适宜的反应条件和影响因素,在最佳条件下,329.2 nm处增强的RLS强度与三苯基锡(TPhT)的浓度呈线性关系.用于三苯基锡化合物的测定,检测限为5.2μg.L-1.方法用于实际水样的测定,回收率为95.8%~107.5%.     

依文思蓝与硫酸依替米星和硫酸奈替米星相互作用的共振瑞利散射光谱及其分析应用

在酸性条件下，酸性双偶氮染料依文思蓝（EB）和药物硫酸依替米星（ETS）、硫酸奈替米星（NETS）各自的共振瑞利散射（RRS）强度十分微弱，但EB与ETS或NETS两者相互作用形成的离子缔合物能显著提高RRS强度并产生新的RRS光谱，EB-ETS和EB-NETS体系均在350-400，680-730nm有两个强的散射带，最大散射峰位于713nm处．RRS强度分别与0．2—8．0pg／mL的ETS和0．4—8．0μg／mL的NETS呈线性关系，据此建立了ETS和NETS的测定方法．该方法有较好的选择性，用于市售ETS和NETS注射液中药物含量和临床血药浓度的快速测定，结果满意．     

Structure-based models of cadherin-mediated cell adhesion: the evolution continues

Cadherins are glycoproteins that are responsible for homophilic, Ca²⁺-dependent cell-cell adhesion and play crucial roles in many cellular adhesion processes ranging from embryogenesis to the formation of neuronal circuits in the central nervous system. Many different experimental approaches have been used to unravel the molecular basis for cadherin-mediated adhesion. In particular, several high-resolution structures have provided models for cadherin-cadherin interactions that are illuminative in many respects yet contradictory in others. This review gives an overview of the structural studies of cadherins over the past decade while focusing on recent developments that reconcile some of the earlier findings.Received 7 January 2004; received after revision 24 February 2004; accepted 4 March 2004     

Sodium resonance lidar observations during 2001 Leonid meteor shower over Wuhan

Here is the first report on the observation of meteor ablation trails with lidar in China. Four long-lived Na ablation trails were observed during the 18/19 Nov. 2001 Leonid meteor shower with a sodium resonance lidar over Wuhan. The mean altitude of the 4 trails is 97.95 km, consistent with Leonid high entry velocity (-72 km/s). The peak density averages about 3380±3633 cm-3, and the abundance is (2.33±1.49)×108 cm-2 , both of which are higher than those previously observed for sporadic meteor trails. The RMS width is 359 m and the meteor's age is 81 min, indicating that they are long duration meteor trails. These observation results are quite different from those of sporadic meteor trails, but comparable to the 1998 and 1999 Leonid report. Five night observations from 17 Nov. to 23 Nov. suggest that the 2001 Leonid meteor shower does not have a significant impact on the abundance of the background Na layer.     

非线性时滞反馈对共振附近动力学行为的影响

研究了一个具有线性和非线性时滞反馈的极限环振子系统1∶3共振双Hopf分岔.通过应用多尺度方法,得到了该1∶3共振的复振幅方程,并通过将其复振幅设为极坐标-笛卡尔混合形式,将其复振幅方程转化为一个三维的实振幅系统.通过研究其实振幅方程,对系统在有非线性时滞反馈和无非线性时滞反馈两种情况下的动力学行为进行了分类和比较.结果显示,在两种情形下,系统有完全不同的动力学行为.     

随机共振结合RobustICA的两阶段结构损伤定位方法

为实现强噪声背景低信噪比环境下的结构损伤识别,提出一种基于非线性随机共振降噪与鲁棒性独立分量分析(RobustICA)的两阶段损伤定位方法.第一阶段,运用非线性随机共振系统对强噪声低信噪比的测量响应进行预处理,以降低背景噪声的干扰并增强结构响应;第二阶段,结合RobustICA提取包含损伤信息的特征分量对结构响应异常进行识别,之后计算归一化的源分布向量(NSDV)的最大值对结构损伤异常进行定位.框架数值算例结果表明,所提出的算法能够较精确实现信噪比为5dB下的结构损伤异常识别与定位.